This invention relates to fittings and more particularly to conduit fittings which form threads on the end of an unthreaded conduit while coupling thereto.
There are presently available various types of thread making fittings. These fittings roll threads as the fitting is tightened onto a conduit. Typically, the fitting includes a sleeve having internal threads. The conduit is slid into the sleeve and the fitting is turned onto the end of the conduit to thereby roll threads on the conduit while making connection thereto. In rolling the threads, it is necessary to apply a great amount of torque to the fitting in order to turn it onto the conduit. It is quite possible to torque the fitting onto the conduit and not know when to stop. Generally, the ability to resist pull-out forces is dependent upon the amount of turns obtained by tightening applied to the fitting. However, it is not possible to determine when the required number of turns have been completed. Furthermore, when applying the fitting in a hurry, the conduit will be inserted into the fitting and only a minimal amount of turns will be completed which will be insufficient to provide the amount of tightening needed to resist the pull-out.
With existing prior art fittings, it is almost impossible to inspect the fitting after installation to determine if it has been properly tightened. Since there is no indication on the conduit to indicate the proper depth to which it has entered into the fitting, nor is there any indication on the fitting itself, it is quite possible that an insufficient amount of conduit has entered into the fitting and insufficient tightening has taken place. Similarly, it is possible that too much tightening has occurred and the excessive amount of tightening has caused a stripping of the threads which will loosen the retention between the conduit and the fitting and will reduce the ability to resist pull-out forces.
In many uses, it is necessary to provide a liquid tight fitting. For example, when using conduits for external electrical connections it is necessary to provide for water tightness between the fitting and the conduits. Many of the prior art conduit fittings use a metal to metal contact between the conduit end and an internal seat on the fitting. For example, U.S. Pat. No. 3,272,539 describes such a metal to metal contact. These contacts are not adequate for a liquid tight fitting under all conditions.